There seem to be quite a few fabulous web-sites now that compile LaTeX online.
I was wondering what techniques these sites used to speed up compilation of documents. It would seem they would be particularly interested in reducing the CPU load from loading the compiler, especially as many of the documents they would be asked to create would be relatively small.
In my experience it seems like the ordinary process for creating a relatively small document with LaTeX, especially XeLaTeX, seems to take a substantial amount of time starting the compiler (e.g. a couple seconds), and a relatively very modest amount of time running it (a few milliseconds).
It would seem then that one could gain tremendous improvements in performance for relatively small documents by running (PDF/Xe)LaTeX as a daemon that produced a number of documents without having to restart the process.
Others seem to have tried this, and it has been discussed (also) on Tex.SE before. The techniques seem to be somewhat dated, and in any case I couldn't get them to work on Linux with XeLaTeX (which just happens to be what I'm using).
Are any of the online compilers using a sort of TeX daemon to compile their documents in the background? Are there any other recent developments in this area? I happen to be personally interested in the XeLaTeX on Linux, but I would love to know more about what is happening in the LaTeX performance area.
There also seems to be quite a bit of discussion about pre-compilation (as seen under eg performance), but I tried it and the benefits do not seem to be as great as that of daemonizing the process (though I would stand to be proven correct!).
Are there other techniques these online services may be using to improve the response time of compilation?